1. Field of the Invention
This invention relates generally to a method and apparatus for transferring a skidbase and a drilling structure from a movable vessel, such as a jack-up platform, to a permanent offshore structure, such as a production platform, and, more particularly, to a method and apparatus for accurately positioning the skidbase relative to the movable vessel during the transfer of the drilling structure from the jack-up platform to the production platform.
2. Description of the Related Art
It is common practice in the drilling of offshore oil wells for a fixed platform to be constructed above a promising field so that a multiplicity of wells may be drilled therefrom. Commonly, after the drilling process has been completed, the drilling portion of the platform is removed from the fixed platform and transported to another fixed platform where the same process is repeated. In this manner, the same drilling apparatus can be advantageously used on numerous fixed platforms. When the drilling apparatus is removed, the platform becomes merely a production platform, no longer having drilling capabilities, but remaining at the well site.
It may occasionally be desirable to again place the drilling apparatus on the fixed, production platform to drill additional wells into the field. Quite often, an increase in the price of oil or natural gas can make a formerly economically infeasible field attractive. Thus, the drilling apparatus is replaced on the fixed platform so that additional wells may be drilled to increase the production of oil or natural gas from the field. Further, it is sometimes desirable that the drilling apparatus be placed on the fixed, production platform so that the existing wells may be "reworked" to maintain a desired level of production.
The immense size of such movable drilling apparatus creates substantial technical difficulties in transporting the drilling apparatus and accurately locating it on the fixed platforms without exorbitant cost. At least one prior art system has been proposed that satisfactorily accomplishes these goals at an economically feasible rate.
For example, U.S. Pat. No. 4,103,503, issued Aug. 1, 1978 to Marvin L. Smith describes a method and apparatus that has been well received in the oil well drilling community.
Smith describes a system for transporting the drilling apparatus from the jack-up platform to the fixed platform in two stages. Before the transfer process begins, the jack-up platform is first positioned adjacent the fixed platform, and then the drilling apparatus is transferred in two separate pieces, a skidbase and a drilling structure.
The skidbase, which includes a bridge, is transferred to the fixed platform. The jack-up platform is then elevated to the same height as the top of the skidbase, and the bridge is connected to the jack-up platform to align skid rails on the top surface of the skidbase with skid rails on the deck of the jack-up platform. The drilling structure is then skidded across the skid rails and onto the skidbase on the fixed platform.
It should be appreciated that while the drilling apparatus is accurately described as immense, the jack-up platform must necessarily be an order of magnitude larger to properly carry the drilling apparatus. Accordingly the difficulty of accurately positioning the jack-up platform so that the bridge can be connected to the jack-up platform is readily apparent.
Smith suggests that fine adjustments to the positioning step can be performed by a releasable hydraulic cylinder that extends between the jack-up platform and the bridge. By alternately extending and retracting the hydraulic cylinder, an experienced operator can move the skidbase until it properly aligns with a pin connection on the jack-up platform.
While this process ma be successfully completed it is a manual, time consuming operation that would be better served by a system that automatically and accurately positions the skidbase at the precise location necessary for alignment between the bridge and the jack-up platform.
The present invention is directed to overcoming or at least minimizing one or more of the problems set forth above.